1. Field of the Invention
The present invention relates to an apparatus and method for manufacturing a particulate resin.
2. Discussion of the Background
In the fields of electronic printing and electrophotography, the demand for producing high resolution images has increased in the market recently. In order to improve the resolution of images and characters printed on paper by an electronic device such as a copier and a printer, a toner needs to be a fine particulate resin having a narrow particle diameter distribution. Therefore, it is necessary to improve the technique for forming uniform fine particulate resins. The conventional apparatus for manufacturing a particulate resin used for a toner typically includes (1) a kneading means for kneading a resin with toner components such as a colorant, a charge controlling agent, a release agent, and a hardening agent; (2) a pulverization means for pulverizing the above-kneaded mixture; and (3) a classification means for classifying the above-pulverized mixture. It is difficult to obtain a fine particulate resin having a narrow particle diameter distribution, which has been required in the market, with the above-mentioned conventional apparatus without a classification process. Although such an apparatus may produce a fine particulate resin having an average particle diameter of about 5 to 8 μm, the particle diameter distribution thereof cannot achieve the desired level. This is because the resin tends to be excessively pulverized. In this case, it is necessary to remove a large amount of undesired ultrafine particles so that the particle diameter distribution achieves the desired level.
In attempting to solve the above problems, published unexamined Japanese Patent Application No. (hereinafter referred to as JP-A) 06-138704 discloses an apparatus for manufacturing a particulate resin in which a raw material mixture is extruded from a kneader, then the extruded raw material mixture is drawn by a roller to have a fiber-like shape, and then the fiber-like raw material mixture is cut by a cutter to provide a fine particulate resin. In particular, the resin included in the raw material mixture is kneaded and heated in the kneader, then the melted resin is extruded with a die to have a string-like shape, then the string-like extruded resin is drawn by a roller to have a fiber-like shape and be solidified, and then the solidified fiber-like resin is cut to provide a fine particulate resin having a narrow particle diameter distribution.
However, the above apparatus has the following drawback. If the extruded resin is, for some reason, ruptured when drawn by a roller to have a fiber-like shape, the fiber-like resin cannot be submitted to the next step cutting process. In this case production of the fine particulate resin may be interrupted. Alternatively, fiber-like resins having a variation in diameter are provided, resulting in producing resin particles having large variations in particle diameter. This leads to the deterioration of manufacturing efficiency of a fine particulate resin on a commercial scale. Further, it is difficult to stably provide a fine fiber-like resin having a diameter of not greater than 10 μm on a commercial scale by the above method including drawing a resin by a roller, unless a specific method (e.g., a method for manufacturing a composite fiber having a sea-island structure using a polymer blend including two incompatible polymers, a method for manufacturing a easily-tearable fiber) is used in combination. It may be substantially impossible for the above-mentioned apparatus to stably and efficiently provide fine fibers of a typical resin, which is not optimized for providing fibers.
In attempting to efficiently produce a fine fiber-like resin, JP-A2002-371427 discloses a melt-blow type fiber spinning die for manufacturing a nonwoven fabric. In this apparatus, a melted resin is extruded from a nozzle together with hot air, and then the extruded resin is introduced to a spinning opening together with cold air so that the resin is cooled to become a fiber. Since the resin is drawn immediately after being discharged from the fiber spinning die, the resultant resin particles have little variation in particle diameter even if the resin is ruptured for some reason.
In JP-A 2004-332130, an attempt is made to apply the above-mentioned fiber spinning die to an apparatus in which a raw material mixture of a toner having a fiber-like shape. In other words, operating and setup conditions of the fiber spinning die for manufacturing a toner are mentioned therein. In particular, the optimum conditions of cooling mechanism, operating temperature, air content for drawing, etc. are disclosed therein.
JP-A 2006-106235 discloses a toner manufacturing apparatus, having a configuration similar to the apparatus disclosed in JP-A 2004-332130, including a melt-mixing part configured to melt-mix a plurality of raw materials of a toner and a fining part configured to produce fine particles of the melt-mixed raw materials, and further including a static mixer configured to keep the mixed state of the melt-mixed raw materials until transported to the fining part.
JP-A 2006-106236 discloses a toner manufacturing method including forming a fiber-like raw material mixture of a toner and cutting the fiber-like raw material mixture to provide the toner, further including controlling the shape of the resultant toner.
In the techniques disclosed in JP-A's 06-138704, 2004-332130, 2006-106235, and 2006-106236, raw materials of a toner are previously well mixed before being subjected to the cutting or pulverizing process so that the resultant toner has a narrow particle diameter distribution. In these cases, the fiber-like raw material mixture is cut or pulverized using a secondary device to provide a fine particulate resin. In other words, these toner manufacturing processes include a fiber spinning process instead of a classification process. Therefore, these toner manufacturing processes do not contribute to simplifying the toner manufacturing process.
Published examined Japanese Patent Application No. (hereinafter referred to as JP-B) 63-053006 discloses an apparatus for manufacturing a fine particulate resin in which a solvent solution of a resin is sprayed and dried so that the resultant fine particulate resin is directly obtained without the pulverization or cutting process. However, solvents potentially have a danger of explosion and are harmful for humans. In addition, solvents tend to produce VOCs, resulting in polluting the environment.
JP-A 2005-004182 discloses a toner manufacturing method including pulverizing a kneaded raw material mixture of a toner having bubbles. It is described therein that this method improves the pulverization efficiency and prevents production of ultrafine particles. However, this method, which may belong to the category of pulverization methods, does not solve the problem of improving the circularity of the resultant toner (i.e., producing a spherical toner).
JP-A 2005-258394 discloses a toner manufacturing method including melting a kneaded raw material mixture of a toner and spraying the melted raw material mixture with a high-pressure gas so that fine particles of the toner are produced. This method does not need to include any of the drying process (i.e., solvent removing process), the cutting or pulverization process, or the classification process, and is capable of directly producing toner particles from the melted raw material mixture. However, no mention is made about the optimum conditions of the apparatus and means for scale-up.
For example, although the optimum method and device for supplying the high-pressure gas for spraying are mentioned, no mention is made about the method and device (i.e., nozzle) for supplying the melted raw material mixture. No mention is also made about means for scale-up. Although means for preventing secondary aggregation of particles is mentioned, no mention is made about means for improving the circularity of the primary particles, which is one of the most important requirements for toners recently.